Structural investigation and response surface optimisation for improvement of kefiran production yield from a low-cost culture medium

Kefiran, a water-soluble heteropolysaccharide with molecular weight of 1.35 x 10(6) Da and a specific optical rotation of +64 degrees (c 1.0, H2O), was isolated from kefir grains grown in cheese whey and further purified through DEAE-Sepharose XK26. Response surface methodology was employed to optimise the culture conditions for kefiran production from kefir grains to be lactose concentration 67 g/l, yeast extract 13 g/l, pH 5.7 and temperature 24 degrees C. Intrinsic viscosity was 5.84 dl/g using the Huggins extrapolation and 5.53 dl/g using the Kramer extrapolation. Monosaccharide analysis revealed that kefiran is composed of glucose (Glc) and galactose (Gal) in a relative molar ratio of 1.0:1.1. Its structural features were elucidated by a combination of FT-IR, methylation and GC-MS analysis, periodate oxidation-Smith degradation, partial acid hydrolysis and NMR spectroscopy (H-1, C-13 and HMBC). The data obtained indicated that kefiran possessed a backbone of (1 -> 6)-linked Glc, (1 -> 3)-linked Gal, (1 -> 4)-linked Gal, (1 -> 4)-linked dc and (1 -> 2,6)-linked Gal, with a branch attached to 0-2 of Gal residues and terminated with Glc residues. (C) 2012 Elsevier Ltd. All rights reserved.